What it can do:I wanted to build an audio mixer for my computer speakers with channel remapping (my computer is on a side of the room) and room correction. This can map any input to any output, has build in Gain, 3 band Equalizer, Room correction, surround module, Volume, Attentuation, Remote controller receiver, 4channel VU meter, LCD display, it can play simple sounds (Tone library) and has 2x 5.1 input, stereo input and build-in bluetooth receiver.

After TDA's there is 6 HEF4051 8 channel Multiplexers that will direct ANY channel to ANY or multiple Speakers (Output from TDA is around 4V - it has internal op-amps, therefore the 4051 is working at around middle range with power 9V)

(Rear left can become front right, front right can be front left ... any way you want)

From the rear speakers the signal goes also to the Surround Board (with two PT2399) and they can be turned on and mapped to surround speakers.

Another Function is STEREO - on 5.1input channels, it can direct front inputs to rear speakers to Fill the room in case rear input is quiet.

Controls:

Menu button, 4 channel select, UP/DOWN + Select buttons are on the front panelWhen you're not in Menu, UP/DOWN is Volume, SELECT will turn on Night Mode (LEDs are OFF, LCD is dimmed).

Whole unit is controlled with universal remote (NEC protocol) and has quite messy but working custom interrupt driven IR procedure with address and command (+ verification).

Everything is displayed on 20x2 LCD display and 4x8 LED Vu meter with animation if signal isn't present

IR setting:If you want to assign address and commands form remote, change debug constant from 0 to 1 and the unit will switch into IR check and will display all codes received on the LCD display. With them codes you can then assign functions to buttons (constants again)

Other:All TDAs have the same I2C address, I used PCA9545 I2C multiplexerTo save some pins - 8 to 3 encoder is used for the switchesand LCD is driven with 74HC595 shift register so are all HEF4051 analog multiplexers and TLC5925 LED drivers - everything with SPI @ 8Mhz (clock / 2)

Switch and IR decoding has its own Interrupt routine (speed) and all other procedures are prioritized in the LOOP

All settings are stored for each input individually (Volume, Mapping, Equalizer ...) and restored every time the input is changed.

All settings (except for volume) are written to EEprom on every change and restored during startup

In original design there was an opamp that was connected to the VU input, but didn't work (bad design) and was replaced with decoupling capacitor (updated in schematics). For better VU acquisition it should be re-designed and added, for lower signals

Quality of sound: I'm not an expert, but I would say great. No noise, perfectly quiet if no signal is present, no interference, no sound (like a bang) if channels are changed, equalizer is working beyond expectations, just great (I'm sure someone will say it can't be because ... )

Guess everybody has moved from audio projects to light flashing and other interesting stuff with arduinosThis is a step back I suppose so no comments yet. let me be the first.Seems like a bit of Overkill for me . I was not able to read the schematic on either site.Since 5 y.o. I have only one ear that works so I hear everything in mono.Would not think you can notice the difference with all your features even with two ears

Guess everybody has moved from audio projects to light flashing and other interesting stuff with arduinosThis is a step back I suppose so no comments yet.

Great project! I agree, this is step back simply because all music moved in digital, MP3 etc. IMHO, it's quite rarely someone needs to regulate anything on pure audio, much easier to do this during uncompressing/ decoding stage. I've been thinking to create something similar, but then I bought MP3 player which do all equalizing - 6 + custom, 3D/ surrounding and cost me 12$, I changed my mind.